Processes for production of furfural



July 29, 1958 E. E. MORSE Em 2,845,441

PROCESSES FOR PRODUCTION OF' FURFURAL Filed Nov. 16, 195512m-Jumanbonn-Omn- INVENTORS Emelson/ Moise Wlfel' l2. Hear-IL B mwMf/XWO ATTORNE United States Patent O PROCESSES FOR PRODUCTION OF FURFURALErwin Emerson Morse, Gorham, and Walter L. Hearn, Berlin, N. H.,assignors to Brown Company, Berlin,

.Application November 16, 195s, sensi No. 547,263

s claims. (c1. 26o-341.9)

This invention relates to methods of producing furfural which issuitable for the manufacture of various chemical materials from wasteliquors. More particularly, it relates to producing furfural by thehydrolysis of waste sulite pulp liquors and especially from hardwoodpulp waste liquors.

While it has been recognized for some time that hardwoods containattractive potential quantities of pentosans which are convertibleultimately to furfural, so far as we are aware no practical or economicprocesses for recovering furfural from hardwood waste liquors haveheretofore been known, despite the several past general, and in someinstances specific, suggestions to recover furfural from hardwood wasteliquors. Certain prior proposals have not proven to be feasible inattempts at commercial, rather than laboratory, production. Otherproposals have been delicient or defective because of low, uneconomicyields, high operating costs, excessive plant costs, operatingdifficulties or a combination of several of such factors.

Accordingly, it is an object of this invention to produce furfural fromacidic hardwood waste liquors and the like by methods which arecommercially and technically feasible while minimizing thecost thereof,while maintain- 2,845,441 VPatented July 29, 1958 The waste liquor 11after removal from the blow pit is fed into steam heated preheater 12wherein the temperature of the liquor is raised to aboutv 350 F.Thereafter liquor 11 is conducted to either one of two small (knockout)pots 14 and 14a wherein the temperature of the liquor is raised to thepreferred hydrolysis point of about 385 F. by steam heating. In knockoutpots 14 andl 14aI a certain amount of solids are deposited on theinternal surfaces thereof, necessitating occasional cleaning.

In a presently preferred procedure, we next pass the heated liquor 11 tothe upper portion of a vertically/.positioned reaction vessel 15containing a plurality of sieve plates or other equivalent means ofinsuring intimate gasliquid contact. High pressuresteam is injected intovessel 15 at a lower portion thereof which serves to maintain thehydrolysis reaction temperature at the needed range of between 347 F.and 420 F. In the particular example now being described the reactiontemperature in vessel 15 was held at 410 F. at an operating'gaugepressure of 261 p. s. i. The injected steam also serves to proing highproduct yields and while avoiding excessive investment and operatingcosts. Further objects of the invention will be in part pointed outhereinafter.

In one of its broader aspects the invention may be said to lie inhydrolyzing waste liquors at such temperature and time conditions thatsubstantial destruction of the furfural or furfural-yielding componentseither by heat, polymerization or combination with other components ofthe waste liquors is avoided. More particularly, we have found that bymaintaining the hydrolysis conditions between about 347 F. and 420 F.(and preferably at 385 F.) for between substantially 40 minutes to 10minutes, a high proportion of the theoretically recoverable quantity offurfural present in the waste liquor may be obtained whilesimultaneously avoiding excessive fouling ofthe equipment used.

Perhaps the features of the invention can best be understood andappreciated by reference to the accompanying drawing which presents asimple iiow plan of a particular sequence of processing steps andmaterials successfully employed.

In the drawing, hardwood sulte waste pulping liquor 11 is derived fromcooking hardwood chips for about l0 hours at 75 p. s. i. pressure; ithas a pH of about 1.8 to 2.8 at 25 C. and has a typical solids contentof 12l4%. Analyses indicate that such liquor contains about 1.2 to 2.2%potential furfural based on the total liquor. It is to be noted thatwhen the cooking liquor is discharged to the blow pit after the cookingis completed a certain amount of free furfural may be flashed oit andlost, thus reducing the potential yield somewhat, although provision maybe made for recovery of such ashed furfural as by use of a surfacecondenser.

vide a current of a stripping gas which sweeps out of the top of vessel1 5 the product crude furfural, lay-products such as methanol,low-boiling acids and so on as well as any small amounts of entrappedliquid.

It is to be noted that the capacity ,of vessel 15, feed point injectionpoints and feed rate are to be selected and adjusted so that theresidence time or hold-up of the liquor 11 in the said vessel variesbetween about 40 minutes at the lower range of reaction temperature andabout 10 minutes at the upper temperature ranges; it is also to be notedthat the operating pressures range respectively between about 114 to 295p. s. i. g. at the operating temperatures lying between 347 and 420 F.Lesser times than the ranges indicated resultindnsuicient conversion to,and recovery of, the desired product furfural. On the other hand greaterresidence times also cause reduced yields of furfural due apparently topolymerization or degradation' of the furfural and perhaps combinationwith other components of the liquor.

Under the conditions indicated, the euent spent liquor contains about0.02% potential furfural and 0.02% actual furfural is conducted to wastedischarge. Itis to be noted that in describing the ow plan set forth inthe drawing, in the interests of simplicity no discussion is made of theparticular arrangement of details of heat exchange, equipmentcharacteristics and the like since the present invention is directed tothe operating criteria indicated above. Those skilled in the art willappreciate that variations may be made in the specific ow plan shown tomeet the requirements of a given mill or plant and to minimize steamconsumption, power consumption and so on.

In our studies and research into the problem of producing furfural fromwaste liquors, we found that, contrary to some indications, it washighly important to maintain the time-temperature conditions in therange indicated. For example, when the hydrolysis temperature exceeded420 F. we found that tar-like solids were rapidly formed in vessel 15 toan extent which quickly plugged up the vessel and rendered continuedoperation impractical and, indeed required shut-downs of the plant inorder to clean out the equipment. We also noted the formation ofundesired coke-like material in the vapor disengaging space in the upperportions of vessel 15.

On the other hand at temperatures below 347 F. the yield of furfural wasquite low and excessive hold-up or residence time in the vessel wasnecessary even to achieve low yields. This in turn required impracticalthroughput rates or the use of reaction vessel 15 of excessively largeand uneconomic size.

We found that using the practical time-temperature operating conditionswe discovered and set forth above, over-all recoveries of the order of53% of the theoretical furfural present in the feed liquor could beobtained and at low or moderate cost.

Returning now to the description of the specific ow plan shown, theefiiuent gases from the top of vessel are condensed in condenser 16 andthe condensate is next steam distilled in column 17 to remove undesiredcontaminating volatile components such as methanol and low boilingacids. The bottoms therefrom which is a crude wet dilute furfural isnext concentrated and puried in one or more distillation columns 18 atatmospheric or less than atmospheric pressure. Preferably the productfurfural, dry and of high purity, is stored under a blanket of inertgas.

From the foregoing it will be understood and particularly by thoseskilled in the art that the description of the specific embodiment of aprocess as described above is intended to be illustrative of theprinciple of the invention and is not intended to unduly limit theinvention, the limits of which are set forth more precisely in theappended claims.

Having now particularly described our invention, what we claim is:

l. The process of producing furfural from acidic hardwood waste liquorwhich comprises establishing and maintaining a hydrolysis-reaction zone,conducting said liquor to said zone, maintaining the liquor in said zoneat a temperature between about 347 F. and 420 F. for a period betweenabout 10 and 40 minutes at an operating pressure lying betweensubstantially 114 and 295 p. s. i. g., removing efuent gas and spentliquor from said zone at predetermined areas thereof which are remotefrom each other, and thereafter separating the product furfural from theeuent gas.

2. The process according to claim 1 where in said acidic hardwood Wasteliquor has an initial pH of not less than 1.8 nor more than 2.8.

3. The process according to claim 1 wherein said waste liquor is fed tosaid zone at an upper portion thereof and said spent liquor is removedfrom said zone at a lower portion thereof.

4. The process of producing and recovering furfural to the extent of atleast of the theoretical content thereof in acidic aqueous liquorsresulting from the cooking of hardwoods which comprises establishing andmaintaining a hydrolysis-reaction zone, conducting said liquor to saidzone, maintaining the liquor in said zone at a temperature between about347 F. and 420 F. for a period between about 10 and 40 minutes at apressure lying between substantially 114 and 295 p. s. i. g., removingeluent gas and spent liquor from said zone at predetermined areasthereof which are remote from each other, thereafter recovering theproduct furfural from the effluent gas.

5. The process according to claim 4 wherein stripping steam is injectedinto said zone to simultaneously maintain said zone temperature and tosweep away volatile reaction products.

References Cited in the le of this patent UNITED STATES PATENTS1,946,688 Groth et a1 Feb. 13, 1934 2,369,655 Boehm Feb. 20, 19452,436,804 Hill Mar. 2, 1948 FOREIGN PATENTS 663,997 Germany Aug. 1l,1939 707,638 Germany lune 28, 1941 719,890 Germany Apr. 21, 1942 740,602Germany Nov. l, 1943 OTHER REFERENCES Hitchcock: Chem. Engr. Progress#9, 44:669-74 (1948).

1. THE PROCESS OF PRODUCING FURFURAL FROM ACIDIC HARDWOOD WASTE LIQUORWHICH COMPRISES ESTABLISHING AND MAINTAINING A HYDROLYSIS-REACTION ZONE,CONDUCTING SAID LIQUOR TO SAID ZONE, MAINTAINING THE LIQUOR IN SAID ZONEAT A TEMPERATURE BETWEEN ABOUT 347*. AND 420*F. FOR A PERIOD BETWEENABOUT 10 AND 40 MINUTES AT AN OPERATING PRESSURE LYING BETWEENSUBSTANTIALLY 114 AND 295 P.S.I.G., REMOVING EFFLUENT GAS AND SPENTLIQUOR FROM SAID ZONE AT PREDETERMINED AREAS THEREOF WHICH ARE REMOTEFROM EACH OTHER, AND THEREAFTER SEPARATING THE PRODUCT FURFURAL FROM THEEFFLUENT GAS.